1. Field of the Invention
The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly to a reflective liquid crystal display device with a memory effect and a driving method thereof.
2. Description of Prior Art
At present, information is widely distributed by use of printed matter; it, however, increases the volume of garbage and promotes exhaustion of forest resource for paper pulp. The present inventors think that these problems can be eased by developing a system of providing information being stored in digital information recording media so that users can get the information by use of display devices such as liquid crystal displays. Accordingly, they have developed an electronic book system using liquid crystal display devices. This system would be applicable to various kinds of information which has been distributed by printed matter, such as books (paperbacks, weekly magazines, monthly magazines, technical papers, etc.), newspapers and advertisements.
Publishers (makers) distribute digital information of books as recording media to users which have (own or rent) a display device of an electronic book system, and each user puts the recording media in the display device to get the information.
In order to attain such a system, the display device must be as small and thin as a book so that the user can use it anywhere. It is, therefore, required to reduce the size of the power source by using a liquid crystal display with a memory effect which consumes little electric power. Also, in order to lighten and thin the display device more, a reflective type which does not require a light source shall be used. In short, a reflective liquid crystal display with a memory effect shall be installed.
A reflective liquid crystal display with a memory effect, however, has a drawback that the response speed to a driving voltage is low. The achievement of the above-described system depends on how this drawback can be overcome. If the response speed can be improved, operation of turning the pages for skimming (operation in a rapid mode) will be possible, and the display device will be as easy to handle as a book and can be used as an electronic book.
Conventionally, low-molecular liquid crystal has been used for liquid crystal displays. In a type which uses glass substrates, when large substrates are used, it is difficult to take a rubbing alignment treatment on the substrates evenly, and consequently, the substrates are fragile. Also, the angle of field of the display area is narrow, and it is difficult to read information displayed thereon. Moreover, if a shock or pressure is applied to the display substrates, the alignment comes out of order, and reading of information becomes impossible. Further, the liquid crystal itself is volatile, and for a display of information, electric power must be supplied to the display device constantly and continuously, that is, the power consumption of the liquid crystal display is large.